In conventional manufacturing and assembly lines, such as those used in the aerospace industry for manufacturing of aircraft, attempts to automate manufacturing and assembly lines generally have been limited to straight-line towing of a nearly completed assembly, such as an airplane. Assembly operations, such as riveting, typically take place in traditional fixed locations, thereby requiring use of a conventional crane to move a carrier containing a work item into position for assembly. For example, assembly jigs are regularly used as carriers in the manufacturing and assembly of bonnets for aircraft. In a conventional aerospace assembly line, an assembly jig might be located in a high bay on the manufacturing floor for pre-riveting operations. When it is time to perform riveting operations, the assembly jig must be lifted using a conventional crane and delivered to an automatic riveting machine found in another work station on the manufacturing/assembly floor. Upon completion of riveting operations on the automatic riveting machine, the assembly jig must again be lifted using the conventional crane and returned to its high bay location.
Loading a carrier for large work items, such as bonnets, onto a conventional crane often requires between 45 minutes and 1 hour of manufacturing/assembly floor time, and this estimated time period presumes that the crane is even available for use in lifting operations. This same estimated amount of time then may be required to return the carrier to its original location in the high bay upon completion of manufacturing/assembly operations, such as riveting. This results in 1½ hours minimum of lost floor time and machine time, resulting in at least 3 hours manufacturing time lost per work item (i.e., bonnet). Further, when the crane is in use, the manufacturing/assembly floor is unable to be effectively used for other manufacturing/assembly operations in order to address safety concerns with respect to workers performing tasks on the manufacturing/assembly floor in proximity to these carriers moving sometimes quite large work items around the floor.